1. Field of the Invention
This invention is related to magnetic domain device apparatus and, more particularly, to improvements for providing a substantial uniform rotational magnetic field distribution for such apparatus.
2. Description of the Prior Art
It is well known that the rotational magnetic field distribution, in the absence of any compensation, generated by the two orthogonal magnetic field drive coils for a magnetic domain device has a peak distribution which has a maximum at the center of the coils and minima at its edges.
One prior art solution for obtaining a uniform rotational magnetic field distribution is to provide a varied separation between adjacent turns of the solenoid in lieu of providing a uniform separation. Thus, for example, in U.S. Pat. No. 4,045,786, the spacing between adjacent turns of the printed circuit encompassing orthogonal solenoid system disclosed therein is gradually decreased proceeding from the center of the particular solenoid to its edges. As is obvious, such prior art systems require careful control to effect the required variable and symmetrical spacing between turns. Moreover, where the solenoids are of the discrete wire wound type, effecting and maintaining the desired variable and symmetrical spacing between turns is even more complex. Furthermore, the variable spacing itself could be a potential source of ripple in the rotational field uniformity.
In the publication entitled "Double Stacked Bubble Memory Module", D. G. McBride, IBM Technical Disclosure Bulletin, Vol. 20, No. 8, January 1978, pp. 3054-3055, it refers to and discusses ripple in the rotational field uniformity caused by spacings between turns of the solenoids of an encompassing orthogonal solenoid system of a first described therein bubble memory package structure. Briefly, the structure includes a planar rectangular substrate on one side of which are mounted the chips and on the other side of which a plurality of input/output terminal pins are extended outwardly normal thereto. More spcifically, the pins are arranged in double parallel rows along each of the four edges of the substrate, with the pins of parallel rows being in columnar alignment. In this structure, the turns of the inner solenoid is wrapped around the chip mounted substrate about two of its parallel edges in the gaps between the columns of aligned pins located along these last two mentioned edges. As a result, the adjacent turns of each solenoid which are wrapped in the gaps have a close normal spacing, whereas the adjacent turns of either solenoid which are wrapped on each side of a column of aligned pins have a much larger spacing. It is this last mentioned spacing that results in the aforementioned ripple.
The publication further describes another structure which overcomes this ripple effect. This other structure has two separate pinned rectangular structures. Each substrate is pinned only along two parallel edges. The chips are mounted on one of the substrates and the inner solenoid is wrapped along its non-pinned parallel edges. Thereafter, the so wrapped substrate is mounted, i.e. stacked, with its pins facing the non-pinned side of the other substrate which carries thereon a pattern of terminal pads in register with the facing pins of the first substrate. The facing pins and pads are bonded together. The terminal pads are interconnected in turn with the heads of the pins carried by the aforementioned other substrate. The outer solenoid is then wrapped over the stacked assembly so that it passes about the non-pinned edges of the solenoid substrate which are orthogonal to the non-pinned edges of the first substrate. As a result, the turns of both of the orthogonal windings of the second structure described in the publication are wrapped with a uniform spacing and without the necessity of passing between pins as in the first described structure of the publication. However, because of the stacking of the substrates, the structure is bulky and complex, and, furthermore, is subject to the aforementioned rotational magnetic field peak distribution which in turn limits the effective active region in which the chips can be mounted.
It has also been suggested that an auxiliary peripheral compensating coil be provided to compensate for the peak distribution of the rotational magnetic field. However, this has the disadvantage of substantially increasing the height of the magnetic domain device apparatus and/or of increasing the power consumption.
It should be understood that it is also known in the prior art to compensate for non-uniformities in the bias magnetic field which are generally produced by the permanent magnet system associated with magnetic bubble devices and which maintain the magnetic domains of the devices. This type of compensation is generally accomplished with additional permanent magnets or high-permeability plates and, as such, are limited to the control of the bias field distribution per se, but not the rotational field distribution, cf. U.S. Pat. Nos. 3,927,397 and 4,068,219, for example.
It should be understood that there are other prior art orthogonal coil systems which are not of the encompassing type. One such prior art system uses two pairs of orthogonal flat coils so that the chips are sandwiched between the two pairs. Another such non-encompassing prior art system, referred to as a reflection coil system, uses a single pair of orthogonal flat coils located on one side of the chips and a coacting single reflective conductive plate located on the other side of the chips, thereby eliminating one of the pairs of orthogonal coils of the aforedescribed two pair system, cf. the publication entitled "Reflection Coil Packaging For Bubble Devices", Masaki Takasu et al, IEEE Trans. On Magnetics, Mag. 11, No. 5, Sept. 1975, pages 1151-1153. In U.S. Pat. No. 4,027,300, entitled "Bubble Memory Package", R. J. Braun, coinventor herein, and assigned to the present assignee hereof, another reflective coil system is described which uses a single pair of orthogonal coils and a pair of reflective conductive plates, one for each coil. The chips are sandwiched between the two plates. The two plates in turn are sandwiched between the two coils. Each coil coacts with plates located on the opposite side of the chips. However, the plates must be orthogonally slotted so that the flux from the particular coil can be channeled through the slots of the adjacent plate and thus coacts with the other plate located on the opposite side of the chips. The aforesaid patent describes non-encompassing systems of the flat coil and solenoid types. It should be noted that non-encompassing systems do not have inner and outer, i.e. encompassing, solenoids per se, and/or chips mounted within any of the coils. Moreover, in the case of prior art reflective coil systems, the reflective conductive plate does not and cannot provide a shield for the flux passing within the center of the coil and, consequently, does not and cannot overcome the problems associated with an encompassing coil system and particularly where the chips are mounted within the inner coil of such an encompassing coil system.